A silent chain is disclosed in the U.S. Pat. No. 4,915,675. According to the specification and drawings of U.S. Pat. No. 4,915,675, a plurality of link plates having engagement teeth engaging with sprocket teeth are disposed in parallel such that a connecting pin is put through holes on the link plates and chained in sequence longitudinally. In a plate row having fewer link plates, guide plates not having teeth engaging with the sprocket teeth, in which both ends of the connecting pin are pressed and fit, are disposed in parallel, and a guide link row having (n+1)plates are formed with other inner plates. A plate row having more link plates forms a joint link row consisting only of (n) link plates not having guide plates.
Therefore, when a tensile load is applied in the longitudinal direction to the silent chain, the load applied on each of the link plates of a joint link row consisting of (n) link plates becomes higher than the load applied on each of two guide plates and (n-1) link plates which form a guide link row of (n+1) plates; and therefore, the link plates of the joint link row are apt to rupture. In the aforementioned U.S. Pat. No. 4,915,675 in view of this problem, the thickness of each of the (n) link plates of the joint link row is made larger than that of each of (n-1) link plates of the guide link row consisting of (n+1) plates, so that the rupture strength of each of two guide plates and (n-1) link plates of the guide link row consisting of (n+1) plates can balance that of each of (n) link plates of the joint link row, thereby avoiding rupture of the link plates of the joint link row.
In the prior art described above, the plates of the guide link row and the joint link row are made balanced in rupture strength and thereby protected from rupture.
However, both ends of the connecting pin are pressed and fit in the holes of the guide plates not having teeth engaging with the sprocket teeth. And, each of the connecting pin holes on the link plates interposed in the guide link row, having teeth engaging with the sprocket teeth, has a free play gap with respect to the connecting pin. And, each of the connecting pin holes on the link plates of the joint link row has a free play gap with respect to the connecting pin. And, if a low tensile load is applied to the guide link row and the joint link row in the longitudinal direction of the chain, the holes for the intermediate link plate G1 and G2 of the guide link row do not come into contact with the connecting pin, as both ends of the connecting pin are pressed and fit in the guide plates. However, the holes for the link plate L1-L3 of the joint link row come into contact with the connecting pin at hole edges K on the opposite side of the direction that the tensile load is working, as shown in FIG. 2.
Next, if a high tensile load is applied to the longitudinal direction to the chain, a deflection is induced on the side of the joint link row which has more link plates engaging directly with the sprocket teeth on the intermediate part of the connecting pin, and as shown in FIG. 3, the intermediate part of the connecting pin deforms largely in a barrel shape towards the side of the joint link row L. Consequently, guide plates GL bend outwardly.
Further, a load working on the hole edges H of the intermediate link plates of the joint link row is lower than the load working on the hole edges E of the link plates on both ends of the joint link row. However, a locally concentrated load is applied on the connecting pin hole edges E on both the outer link plate L2, L3 of the joint link row L, due to end tooth bearing accompanied by the barrel-shaped deformation of the connecting pin. Abrasions of the connecting pin and the hole edges E of the link plates are enlarged, which can cause not only abrasion stretch in the chain, but also rupture due to an unbalanced load.